The hypotheses tested in this study are: 1) Systemic hypertension in the immediate postoperative period is detrimental to coronary artery blood flow and to myocardial metabolism, 2) The ideal level of systemic arterial pressure with regard to myocardial metabolism can be determined using a thermodilution flow catheter placed in the great cardiac vein, 3) Mode of pacing may effect myocardial metabolism. Prior to operation the coronary sinus and great cardiac vein are cannulated with a Thermister catheter. Serial determinations of coronary flow, lactic acid concentrations and a host of hemodynamic variables are made before and after coronary artery bypass. In the postoperative interval, systemic blood pressure is altered to assess myocardial metabolism at various levels. Various modes of pacing are used to determine the effects on myocardial metabolism. These studies should determine the efficacy of blood pressure control and pacing mode on myocardial metabolism in the immediate postoperative interval after coronary artery bypass and other procedures.